1. Field of the Invention
The present invention relates to moisture-curable compounds containing isocyanate and alkoxysilane groups, which can be cured in the presence of moisture to form coatings and sealants.
2. Description of the Prior Art
It is known that polyisocyanate resins are curable in the presence of atmospheric moisture to form polyurea coatings. During the curing mechanism an isocyanate group reacts with moisture to form an amino group, which then reacts with another isocyanate group to form a urea group. One of the disadvantages of these moisture-curing resins is that the curing mechanism is relatively slow.
It has been suggested in U.S. Pat. Nos. 3,420,800 and 3,567,692 that the curing rate of moisture-curable polyisocyanates can be increased by incorporating either aldimines or ketimines. It is stated that the reaction of moisture with an aldimine or ketimine to form the corresponding amine is faster than the reaction of moisture with an isocyanate group to form an amine. A disadvantage of the use of aldimines and ketimines to accelerate the cure of polyisocyanates is that it requires the preparation of an additional component and requires some type of metering equipment to ensure that the two components are blended in the proper proportions.
It is an object of the present invention to increase the curing rate of moisture-curable polyisocyanates without the need for a co-reactant.
This object may be achieved with the polyisocyanates of the present invention, which have been modified to contain alkoxysilane groups incorporated through secondary amino groups. The faster curing rates obtained according to the present invention are surprising because alkoxysilane groups, which are also curable in the presence of moisture, cure more slowly than polyisocyanates. However, when both isocyanate groups and alkoxysilane groups are present, a faster curing rate is obtained.
U.S. Pat. Nos. 4,687,533 and 5,623,044 disclose the preparation of compounds containing isocyanate groups and alkoxysilane groups by reacting a portion of the isocyanate groups with amino compounds containing two trialkoxysilane groups. To the contrary the present invention only allows for the presence of such amino compounds when the moisture-curable compounds also contain repeating ethylene oxide units. In addition, these patents failed to recognize the improvement in curing rate that can be obtained with the moisture-curable compounds of the present invention.
U.S. Pat. Nos. 4,067,844 and 4,374,237 disclose the preparation of compounds containing isocyanate groups and alkoxysilane groups by reacting a portion of the isocyanate groups of NCO prepolymers with amino compounds containing alkoxysilane groups. The moisture-curable compounds according to the present invention must prepared from polyisocyanate adducts as opposed to NCO prepolymers.
Copending application, U.S. Ser. No. 09/058,072, discloses water dispersible compounds containing isocyanate and alkoxysilane groups. The water dispersible compounds must be prepared from a polyisocyanate component having a minimum average functionality of 2.4 and be rendered water dispersible by the use of either ionic or nonionic hydrophilic groups.
Copending application, U.S. Ser. No. 08/992,551, discloses the preparation of polyurethane-urea dispersions containing alkoxysilane groups incorporated through secondary amino groups. However, because the resulting polyurethane dispersions are dispersed in water, they do not contain any unreacted isocyanate groups. In addition, the polyurethane dispersions are prepared from monomeric polyisocyanates as opposed to the polyisocyanate adducts required by the subject application.